Air bars of the general type to which this invention relates are disclosed in U.S. Pat. No. 3,549,070, issued Dec. 22, 1970 to Frost et al; U.S. Pat. No. 3,873,013, issued Mar. 15, 1975 to P. H. Stibbe; U.S. Pat. No. 3,776,440, issued Dec. 4, 1973 to Frost et al; U.S. Pat. No. 3,964,656, issued June 22, 1976 to T. A. Hella; the application of R. A. Daane, Ser. No. 950,745, filed Oct. 12, 1978 (now U.S. Pat. No. 4,197,973 issued Apr. 15, 1980) and the application of P. H. Stibbe, Ser. No. 950,746, filed Oct. 12, 1978 (now U.S. Pat. No. 4,197,971 issued Apr. 15, 1980), all of which have a common assignee herewith.
As brought out in these prior disclosures, such air bars are usually mounted both above and below a web that is moving through a dryer section of a printing press or the like. The air bars that are above the web direct air down onto its upper surface to dry it. The air bars below the web direct air upwardly against it to floatingly support the web as well as to dry its lower surface. Usually there are several air bars both above and below the web, each oriented to have its length extend across the width of the web. Since every air bar must direct an even, uniform flow of air towards the web, all across its width, all of the air bars, both above and below the web, are usually identical with one another.
A typical air bar has two air outlet slots that open from it in a forward direction--that is, towards the web--and those outlet slots extend all along the length of the air bar, parallel to one another, being spaced apart by a small distance across the air bar. For satisfactory flotation of the web, the air streams issuing from the outlet slots are usually in somewhat convergent relation, but it is important that they be symmetrical to a plane that lies between the outlet slots and extends forwardly from the air bar to the web, normal to the web surfaces. Preferably, too, they should have no component of flow in a direction lengthwise of the slots. In prior air bars, pressure air that was to issue forwardly from these outlet slots usually entered the hollow interior of the air bar at its rear; and although the pressure air inlets were in symmetrical relation to the outlet slots, the air entered those inlets from a header in which its flow direction was transverse to the length of the air bar and thus in asymmetrical relation to the two slots. As a result, much attention had to be given to the provision of means in the interior of the air bar for ensuring that like flows would issue from the two outlet slots.
The above mentioned Hella U.S. Pat. No. 3,964,656 relates to an air bar that had its pressure air inlet at one of its ends, but here again the inflow of pressure air was in symmetrical relation to the outlet slots although markedly asymmetrical to the mid-point in the length of the bar.
There are installations in which, for one reason or another, it is not feasible to introduce pressure air into every air bar from its rear or from one of its ends, and wherein the pressure air must instead be fed into the air bar from one side thereof, in a direction markedly asymmetrical to the outlet slots. Having in mind that it has always been considered somewhat difficult to get like flows out of the two outlet slots when pressure air was brought into an air bar in a flow that was in reasonably symmetrical relation to them, it will be understandable that there was all the more difficulty with a pressure air inflow that came from one side of the plane of symmetry of the outlet slots.
The general object of the present invention is to provide an air bar of the type that has two parallel lengthwise extending air outlet slots opening from its front, which air bar is so arranged that substantially identical air streams issue from the two outlet slots, the air issuing from each slot flows in a direction normal to the length of the slot, and each of said air streams has a desired velocity profile along the length of the outlet slot--and all of this notwithstanding that pressure air may enter the hollow interior of the air bar through an air inlet which is in markedly asymmetrical relation to the plane of symmetry of the two outlet slots and/or the midpoint along the length of the air bar and/or with a flow direction markedly different from that desired in the air streams issuing from the slots.
It is a more specific object of the invention to provide flow distributor means for an air bar of the character described whereby pressure air which enters the interior of the air bar at one or a few locations at one side thereof is so redirected and redistributed that it is caused to emerge in substantially identical, uniform streams from a pair of forwardly opening air outlet slots that extend along the length of the air bar.
Another object of this invention that will be understood to have great practical importance is to provide an air bar having flow distributing means whereby like air flows are caused to issue from both outlet slots of the air bar even though pressure air is fed into the air bar in very asymmetrical relation to those slots, which air bar comprises a substantial number of components common to air bars that have heretofore had substantial commercialization, particularly air bars such as are disclosed in the above-mentioned Hella Pat. No. 3,964,656 and the Stibbe application Ser. No. 950,746.